JP2006054675A - Ofdm receiver and ofdm signal repeater system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM receiver for obtaining a reception signal whose quality is satisfactory at the time of diversity-receiving an OFDM signal. <P>SOLUTION: This OFDM receiver is provided with a propagation path estimating part 108 for estimating propagation path characteristics in the frequency region of each antenna branch on the basis of the FFT output signals of respective antenna branch processing units BR-1 to BR-N, a signal quality estimating part 109 for estimating the signal quality of each antenna branch on the basis of the output signal of the propagation path estimating part 108, a multiplying part 110 for multiplying the propagation path characteristics and the signal quality by corresponding branches, and a composition part 107 for performing weighting composition of the FFT output signals on the basis of the multiplication result. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an OFDM receiver that receives radio signals transmitted by an orthogonal frequency division multiplexing (OFDM) system with a plurality of antennas and performs diversity combining to improve reception performance, and OFDM. The present invention relates to an OFDM signal relay apparatus that converts a received signal into a radio signal again and relays it.

  Conventionally, a technique for receiving OFDM signals with a plurality of antennas and combining them with diversity is known as a method of reducing the influence of multipath by combining signals after discrete Fourier transform for each subcarrier. (For example, refer to Patent Document 1). This utilizes the feature of OFDM that if the multipath delay time is within the guard interval, intersymbol interference does not occur. By combining each subcarrier, carrier power-to-noise ratio (C / N) can be effectively improved.

  However, Patent Document 1 does not consider the influence of automatic gain control generally used in an OFDM receiver. When receiving OFDM signals, analog / digital conversion is performed on signals affected by distance attenuation and fading in radio propagation, so automatic gain is used for the purpose of ensuring bit accuracy in the analog / digital converter. Generally, control is performed. By this automatic gain control, a signal having a different reception level for each antenna is controlled to be the same at the time of input to the analog / digital converter. As a result, signals with different signal-to-noise ratios for each antenna are input to the demodulation unit at the same level.

  Specifically, Patent Document 1 does not consider that the signal-to-noise ratio differs between output systems (branches) from each antenna in the weighting coefficient W1 (k) used when diversity combining is performed. .

As a diversity reception method considering the influence of this automatic gain control, a signal-to-noise ratio of a signal input to the combining unit is estimated, and a weighting amount for each branch is determined according to the estimated value. Alternatively, a configuration is also known in which instead of estimating the signal-to-noise ratio, the input level in the automatic gain control circuit is input to the synthesis unit, and the weighting amount for each branch is changed in accordance with the input level (for example, a patent) Reference 2).
JP 2002-271291 A JP 2003-110521 A

  However, although the weighting amount for each branch can be defined in the conventional configuration, the maximum ratio combining with different weighting amounts for each subcarrier cannot be performed. As a result, there is a problem that the reception performance deteriorates particularly in a multipath environment. In other words, subcarriers whose power is reduced due to multipath and the like are also amplified by the equalization circuit, and all subcarriers are combined at the same ratio after equalization, so even subcarriers with a low signal-to-noise ratio are uniformly distributed. It will be synthesized.

  In addition, since an equalization circuit that compensates for transmission path distortion due to multipath is provided in each branch, there is a disadvantage that the circuit scale is increased accordingly. Furthermore, since it is necessary to execute a proportional operation for determining the composition ratio between branches several times, a plurality of division operation units having a relatively large circuit scale are provided. For this reason, there is a drawback that the circuit scale is increased by this amount. In addition, there is a drawback that sufficient accuracy cannot be obtained when estimating the signal-to-noise ratio of the signal input to the synthesis unit.

  The present invention has been made in view of this point, and an object of the present invention is to provide an OFDM receiver capable of obtaining a high-quality received signal with a small circuit scale when receiving an OFDM signal with diversity. It is another object of the present invention to provide a small-sized OFDM signal relay apparatus that can obtain a relay signal with high quality in an OFDM signal relay apparatus that converts a OFDM signal received with diversity again into a radio signal and relays it.

  In order to solve such a problem, the present invention provides an OFDM receiver for diversity receiving OFDM signals, and each antenna branch based on the output signals of Fourier transform means of each antenna branch processing unit having a plurality of antennas and automatic gain control means. Channel estimation means for estimating the channel characteristics in the frequency domain, and a signal for estimating the signal quality of each antenna branch based on the output signal of the channel estimation means and the output signal of the Fourier transform means of each antenna branch processing unit Quality estimation means, multiplication means for multiplying the corresponding channel quality of each antenna branch obtained by the propagation path characteristics obtained by the propagation path estimation means and signal quality estimation means between corresponding branches, and a plurality of antennas Multiply the output signal of the Fourier transform means of the branch processing unit To be provided with a combining means for weighting and combining based on a multiplication result obtained by the means.

  As a result, the signal quality estimation means obtains the signal strength at the time of reception of each branch lost for gain control by the automatic gain control means, and the multiplication means obtains the subcarrier reflecting the signal strength at the time of reception. Since the weighting factor for each is obtained, the synthesis unit obtains a synthesized signal for each subcarrier that reflects the signal strength at the time of reception.

  According to the present invention, since the signal strength (signal quality) at the time of reception of each antenna branch lost by the automatic gain control means can be reflected and the signal for each subcarrier can be combined, Be able to get. Basically, it is not necessary to separately provide an equalization circuit, so that it is possible to realize an OFDM receiver capable of obtaining a reception signal for each subcarrier with a high quality with a simple circuit configuration. Furthermore, by providing such an OFDM receiver in the OFDM repeater, a small OFDM signal repeater that can transmit a relay signal with good quality can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(1) Embodiment 1
FIG. 1 shows the configuration of an OFDM receiving apparatus according to Embodiment 1 of the present invention. The OFDM receiver 100 includes N reception antennas 101-1 to 101-N, N reception conversion units 102-1 to 102-N, and N automatic gain control units (AGC) 103-1 to 103. -N, N analog / digital converters (A / D) 104-1 to 104-N, N orthogonal demodulators 105-1 to 105-N, and N fast Fourier transform units (FFTs) ) 106-1 to 106-N, a synthesis unit 107, a propagation path estimation unit 108, a signal quality estimation unit 109, and a multiplication unit 110.

  That is, in the first embodiment, a reception system (branch) is connected to each of the N reception antennas 101-1 to 101-N, and the N branch processing units BR-1 to BR in the entire apparatus. -N is provided. Each branch processing unit BR-1 to BR-N includes a reception conversion unit, an automatic gain control unit (AGC), an analog / digital conversion unit (A / D), an orthogonal demodulation unit, and an FFT. This is the same configuration as a general OFDM receiver.

  Reception conversion sections 102-1 to 102-N frequency-convert radio frequency signals to an intermediate frequency band (IF band). The automatic gain control units (AGC) 103-1 to 103 -N control the IF band signals so as to have a constant level, and remove the influence of thermal noise and the like outside the signal band by a channel filter (not shown). The signals set to a constant level are subjected to analog / digital conversion by A / Ds 104-1 to 104-N, then orthogonally demodulated by orthogonal demodulation units 105-1 to 105-N, and Fourier-transformed by FFTs 106-1 to 106-N. Converted. Incidentally, a guard interval removing unit (not shown) is provided in the preceding stage of the FFTs 106-1 to 106-N, and only the effective symbols excluding the guard interval length are processed in the FFTs 106-1 to 106-N.

  The outputs of FFTs 106-1 to 106-N are sent to combining section 107 and propagation path estimating section 108.

  The propagation path estimation unit 108 estimates the frequency characteristics of the entire signal band (all subcarriers) based on the pilot carrier, and sends the estimation result to the multiplication unit 110 as the propagation path characteristics Hn (k). In this embodiment, the propagation path estimation unit 108 also sends the propagation path characteristic Hn (k) to the signal quality estimation unit 109.

  The signal quality estimation unit 109 estimates the signal quality (signal band noise ratio) of each branch based on the propagation path characteristic Hn (k), and sends the estimation result Qn to the multiplication unit 110.

  The multiplier 110 multiplies the propagation path estimation result Hn (k) for each antenna branch and each subcarrier by the signal quality estimation result Qn for each antenna branch. Specifically, the multiplying unit 110 transmits the channel characteristics Hn (k) for each subcarrier of each antenna branch obtained by the propagation path estimating unit 108 and the signal of each antenna branch obtained by the signal quality estimating unit 109. The quality estimation value Qn is multiplied between corresponding branches. The multiplication result can be said to be a propagation path estimated value reflecting the input signal level to each of the antennas 101-1 to 101 -N. The multiplication unit 110 sends the multiplication result obtained thereby to the synthesis unit 107.

  The combining unit 107 weights and combines the FFT output signals of the plurality of antenna branch processing units BR-1 to BR-N for each subcarrier based on the multiplication result obtained by the multiplying unit 110, thereby generating the combined signal S1. obtain.

  Next, the operation of OFDM receiving apparatus 100 according to the present embodiment will be described.

  Here, a case where an ISDB-T system signal which is a Japanese terrestrial digital broadcasting system is received will be described as an example. In the ISDB-T system, signals called scattered pilots (SP) are transmitted at regular intervals in the frequency domain. It is possible to estimate the frequency characteristic between SP signals based on this SP signal. For example, a method of linearly interpolating between SP signals, a method of interpolating between SP signals by inserting a zero between SP signals and then inputting to a low-pass filter are known.

  The propagation path estimation unit 108 of the OFDM receiving apparatus 100 obtains the frequency characteristics (propagation path characteristics) Hn (k) of the entire signal band by performing such estimation (n: branch number, k: subcarrier number). .

  Multiplier 110 multiplies estimated channel characteristic Hn (k) by signal quality estimation result Qn. Here, the propagation path characteristic Hn (k) differs for each subcarrier, but the signal quality estimation result Qn is the same scalar value for all the subcarriers in the same symbol.

The combiner 107 receives the output Hn (k) × Qn from the multiplier 110 and the FFT output signal Dn (k). Here, when the maximum ratio combining is performed by the combining unit 107, the combined output S1 can be expressed as the following equation.

  The combining method is not necessarily limited to the maximum ratio combining. For example, selective synthesis or equal gain synthesis may be performed. In the case of selective synthesis, the circuit scale can be slightly reduced as compared with the maximum ratio synthesis, but the performance deteriorates. In the case of equal gain combining, the circuit scale is increased and the performance is deteriorated compared to the maximum ratio combining, so it is not practical. In the case of selective synthesis, only the signal of the branch having the largest output Hn (k) × Qn from the multiplier 110 may be used, and the other branches may be set to zero.

  The combined signal S1 is sent to a determination unit (not shown). The determination unit compares the signal point distance between the signal point of the combined signal and a plurality of ideal signal points, and outputs the most probable ideal signal point. In order to perform soft decision maximum likelihood decoding, the distance between signal points from the ideal signal point may also be output.

  Thus, according to the configuration of the present embodiment, the propagation path estimation unit 108 that estimates the propagation path characteristics in the frequency domain of each antenna branch based on the FFT output signal of each antenna branch processing unit BR-1 to BR-N; A signal quality estimation unit 109 that estimates the signal quality of each antenna branch based on the output signal of the propagation path estimation unit 108, a multiplication unit 110 that multiplies the corresponding channel characteristics and signal quality between the corresponding branches, and an FFT output signal. The signal quality estimation unit 109 receives each branch lost due to gain control by the automatic gain control units 103-1 to 103-N. The signal strength at the time is obtained, and the multiplier 110 obtains a weighting factor for each subcarrier reflecting the signal strength at the time of reception. In section 107, the signal strength upon reception or synthetic signal S1 for each subcarrier is reflected is obtained.

  As a result, since the signal strength (signal quality) at the time of reception of each antenna branch lost by the automatic gain control units 103-1 to 103 -N can be reflected, a signal for each subcarrier can be synthesized. A good received signal can be obtained.

  Basically, it is not necessary to separately provide an equalization circuit, so that a reception signal for each subcarrier with high quality can be obtained with a simple circuit configuration.

(1-1) Other configuration example 1
In the embodiment described above, the channel quality Hn (k) obtained by the channel estimator 108 is input to the signal quality estimator 109, and the signal quality estimator 109 uses the signal quality based on this Hn (k). As described in the case of obtaining the estimated value Qn, as shown in FIG. 2, in addition to the channel characteristic Hn (k) obtained by the channel estimating unit 108, the FFT output signal Dn is also input to the signal quality estimating unit 109. Then, the signal quality estimation unit 109 may obtain the signal quality estimation value Qn using the FFT output signal Dn. By doing in this way, it becomes possible to obtain the signal quality estimated value Qn with higher accuracy than the above-described embodiment.

  In this case, for example, the signal quality estimation unit 109 compensates the distortion component of the FFT output Dn (k) using the propagation path characteristic Hn (k), obtains the distance from the ideal signal point in the compensated signal, The signal quality estimation value Qn can be obtained by accumulating the sum of the components.

に示すように、伝搬路特性Ｈｎ（ｋ）でＦＦＴ出力信号Ｄｎ（ｋ）を除することで歪成分を補償し、補償後の信号の雑音成分を求め、これを伝搬路特性Ｈｎ（ｋ）の電力で重み付けしたものをすべてのサブキャリア（Ｎｄ個）にわたって累積する。 That is, the signal quality estimating unit 109

As shown, the distortion component is compensated by dividing the FFT output signal Dn (k) by the propagation path characteristic Hn (k), the noise component of the compensated signal is obtained, and this is obtained as the propagation path characteristic Hn (k). Are weighted over all subcarriers (Nd).

  Incidentally, weighting by the power of the propagation path characteristic Hn (k) may be omitted, but in this case, the estimation accuracy deteriorates. In order to reduce the circuit scale, the absolute value sum of the complex amplitudes of Hn (k) may be used instead of the power of Hn (k). In addition, the cumulative number is not limited to all subcarriers (Nd), but it is also preferable to limit the cumulative number to a number with sufficient accuracy. When the cumulative number is limited, the FFT output signal Dn (k) and the propagation path characteristic Hn (k), which are input signals to the signal quality estimation unit 109, can be similarly limited, which is preferable. .

のように伝搬路特性Ｈｎ（ｋ）の合計電力を乗じておくと、ＡＧＣ出力においてブランチ間のレベルが異なる場合にも適切な信号品質推定値Ｑｎを得ることができ、好適である。本実施の形態では各ブランチの信号品質を推定しているため、ブランチ毎に同一チャネル干渉比が異なっている場合、干渉の大きいブランチほど信号品質が悪いものとして後段の合成部１０７で小さな合成比率で合成されることとなる。すなわち、伝搬路特性Ｈｎ（ｋ）の合計電力を乗じておくことで、受信信号強度だけでは判断できない妨害等の影響も最小化させることが可能となり、妨害等に強い合成が可能となる。 Further, in the signal quality estimation unit 109, the following equation:

Multiplying the total power of the propagation path characteristics Hn (k) as described above is preferable because an appropriate signal quality estimation value Qn can be obtained even when the level between branches differs in the AGC output. In this embodiment, since the signal quality of each branch is estimated, when the same-channel interference ratio is different for each branch, it is assumed that the signal quality is worse for the branch with the larger interference, and the subsequent combining unit 107 has a smaller combining ratio. Will be synthesized. In other words, by multiplying the total power of the propagation path characteristic Hn (k), it is possible to minimize the influence of interference and the like that cannot be determined only by the received signal strength, and it is possible to combine strongly against interference and the like.

(1-2) Other configuration example 2
In the above-described embodiment, the case where the signal quality estimation unit 109 obtains the signal quality estimation value Qn based on the propagation path characteristic Hn (k) has been described. However, the FFT output is performed without using the propagation path characteristic Hn (k). The signal quality estimation value Qn may be obtained using only the signal Dn (k). That is, in FIG. 2, the signal line from the propagation path estimation unit 108 to the signal quality estimation unit 109 may be omitted.

  In this case, for example, it is preferable to input the FFT output signal Dn (k_SP) of only the SP signal to the signal quality estimation unit 109 (k_SP: subcarrier number in which SP exists). In this case, the signal quality estimation unit 109 includes an FFT 301, a square unit 302, a comparison unit 303, a threshold setting unit 304, an accumulation unit 305, and an inverse number calculation unit 306, for example, as shown in FIG. And it is sufficient.

  In the configuration of FIG. 3, for example, when an SP signal for one symbol is input in the 13-segment ISDB-T system, the number of SPs is 468. deep. The signal quality estimation unit squares the result of the FFT performed by the FFT 301 by the squaring unit 302. The comparison unit 303 outputs only components smaller than the threshold set by the threshold setting unit 304 to the subsequent accumulation unit 305. As the threshold value, it is preferable to set a value with which sufficient accuracy can be obtained even in the worst signal band-to-noise ratio assumed as a receiving device or a relay device. Here, outputting only the component below the threshold corresponds to outputting only the noise component to the subsequent stage. The accumulating unit 304 obtains the power sum of the input values, obtains the reciprocal of the accumulated result, and sends this to the multiplying unit 110 as the signal quality estimated value Qn.

(2) Embodiment 2
FIG. 4, in which parts corresponding to those in FIG. 1 are assigned the same reference numerals, shows the configuration of the OFDM receiving apparatus according to Embodiment 2 of the present invention. The OFDM receiving apparatus 400 replaces the signal quality estimation unit 109 in the configuration of FIG. A / D) 401 is provided.

  Here, in the automatic gain control sections 103-1 to 103 -N, control is performed so that the output value becomes a constant level. For this reason, the control voltage S10 of the automatic gain control units 103-1 to 103-N is a value corresponding to the input level to the automatic gain control units 103-1 to 103-N.

  The OFDM receiver 400 performs analog / digital conversion on the control voltage S10 in each branch, and then inputs the signal to the multiplier 110 as the signal quality estimation value Qn. Thus, the multiplication unit 110 can obtain a multiplication result reflecting the input signal level to each branch, that is, a propagation path characteristic for each subcarrier reflecting the input signal level to each branch. As a result, the combining unit 107 can synthesize the signal for each subcarrier while reflecting the signal strength (signal quality) at the time of reception of each antenna branch lost by the automatic gain control units 103-1 to 103 -N. become able to. As a result, it is possible to obtain a composite signal S3 with good reception quality.

  Thus, according to the present embodiment, the propagation path estimation unit 108 that estimates the propagation path characteristics in the frequency domain of each antenna branch based on the FFT output signal of each antenna branch processing unit BR-1 to BR-N, and each antenna A second analog / digital converter 401 for analog / digital conversion of the control voltage S10 in the automatic gain controllers 103-1 to 103-N of the branch processing units BR-1 to BR-N, propagation path characteristics and control voltage data; As in the first embodiment, a simple configuration is provided by providing a multiplying unit 110 that multiplies the corresponding branches with each other and a combining unit 107 that weights and synthesizes the FFT output signal for each subcarrier based on the multiplication result. Thus, it is possible to realize the OFDM receiver 400 that can obtain a better synthesized signal S3.

  The analog / digital conversion unit 401 needs to be capable of converting the number of N branches. However, the analog / digital conversion unit 401 is not necessarily converted at the same timing, and may be of a serial conversion type.

  Further, since the control voltage value in the automatic gain control units 103-1 to 103-N is an output of an analog element, an error due to individual difference is assumed. Therefore, the individual difference is measured in advance, as shown in FIG. It is more preferable to provide conversion tables (look-up tables) 501-1 to 501-N for correcting errors due to the individual differences after the analog / digital conversion unit 401.

  Further, in order to correct an error due to a temperature change, as shown in FIG. 6, individual differences of the automatic gain control units 103-1 to 103-N are compensated corresponding to a plurality of temperatures in the subsequent stage of the analog / digital conversion unit 401. It is more preferable to provide a plurality of conversion tables (look-up tables) 601a to 601c. In this case, the temperature detected by the temperature sensor 601 is digitized by an analog / digital conversion unit (A / D) 603 and input to the switching unit 604. The switching unit 604 determines the temperature region detected by the temperature sensor 602, and selects a conversion table corresponding to the determined temperature region from the plurality of conversion tables 601a to 601c. As a result, the output of the analog / digital conversion unit 401 is subjected to temperature compensation and individual difference correction by the conversion table selected by the switching unit 604 and is sent to the multiplication unit 110.

  Needless to say, when the control voltage values in the automatic gain control units 103-1 to 103-N are inversely proportional to the input level, reciprocal calculation is necessary. In addition, a log amplifier is inserted to convert the log amplifier output from analog to digital so that the control voltage value in the automatic gain control units 103-1 to 103-N becomes a logarithmic scale value with respect to the input level, and the converted digital signal is converted to digital. It is also preferable that the signal is converted again into a linear scale value.

  Furthermore, in this embodiment, instead of the signal quality estimation unit 109, an analog / digital conversion unit (A / D) 401 that performs analog / digital conversion of the control voltage in the automatic gain control units (AGC) 103-1 to 103-N. The analog / digital conversion unit (A / D) 401 that performs analog / digital conversion of the control voltage in the automatic gain control units (AGC) 103-1 to 103 -N and the signal quality estimation unit 109 are described. It is good also as a structure which calculates | requires signal quality Qn using both.

(3) Embodiment 3
FIG. 7 shows the configuration of an OFDM relay apparatus according to the third embodiment. The OFDM relay apparatus 700 receives an inverse Fourier transform unit (IFFT) that receives the combined signal S1 (S2, S3) obtained by any of the OFDM receiving apparatuses 100 (200, 400) described in the first, second, or third embodiment. ) 701, a quadrature modulation unit 702, a digital / analog conversion unit (D / A) 703, a transmission conversion unit 704, and a transmission antenna 705.

  The OFDM relay apparatus 700 is divided into subcarriers by the OFDM receiving apparatus 100 (200, 400) by inputting the output signal S1 (S2, S3) of the combining unit 107 of the OFDM receiving apparatus 100 (200, 400) to the IFFT 701. The received signal is returned to the time axis signal. The IFFT output signal is subjected to quadrature modulation by a quadrature modulation unit 702 after a guard interval is added by a guard interval addition unit (not shown). The output of the quadrature modulation unit 702 is digital / analog converted by the D / A 703, then up-converted to a radio frequency band by the transmission conversion unit 704, and output from the transmission antenna 705 as a relay signal. Of course, the total filter characteristics in the orthogonal modulation unit 702 and the transmission conversion unit 704 are designed so that the relay signal to be transmitted satisfies the transmission spectrum mask defined in the specification or the like.

  According to the present embodiment, the OFDM signal receiving apparatus 100 (200, 400) proposed in the first or second embodiment is provided in the OFDM relay apparatus, so that a good combined signal S1 (S2, S3) is obtained. Therefore, it is possible to realize a small OFDM relay apparatus 700 that can form a good relay signal.

  As shown in FIG. 8, a determination unit 801 for determining the combined signal S1 (S2, S3) output from the OFDM receiving apparatus 100 (200, 400) is provided, and once determined, it is input to the IFFT 701. Good. This is effective as a method that takes advantage of the system premised on performing error correction decoding on the receiving terminal side.

(4) Embodiment 4
FIG. 9, in which the same reference numerals are assigned to corresponding parts as in FIG. 1, shows the configuration of the OFDM relay apparatus according to Embodiment 4 of the present invention. The OFDM relay apparatus 900 includes N reception antennas 101-1 to 101-N, N antenna branch processing units BR-1 to BR-N, a channel estimation unit 108, a signal quality estimation unit 109, Multiplier 110, FIR (Finite Impulse Response) filters 901-1 to 901-N, adder 902, inverse fast Fourier transform (IFFT) 903-1 to 903-N, and orthogonal modulator 702, a digital / analog conversion unit 703, a transmission conversion unit 704, and a transmission antenna 705.

  The OFDM relay apparatus 900 according to the present embodiment performs addition in the time axis domain instead of the synthesis in the frequency domain described in the first and second embodiments. Specifically, the time axis is obtained by inverse Fourier transforming the weighting factors for each branch sent from the multiplication unit 110 to the synthesis unit 107 in FIGS. 1, 2, and 4 using IFFTs 903-1 to 903 -N, respectively. Convert to area. Then, the weighting coefficient converted into the time axis region is supplied to the FIR filters 901-1 to 901 -N provided in the corresponding branches.

  The FIR filters 901-1 to 901 -N receive the outputs of the quadrature demodulation units 105-1 to 105 -N of each antenna branch, and the outputs of IFFTs 903-1 to 903 -N as coefficient inputs. As a result, the FIR filters 901-1 to 901-N filter the outputs of the orthogonal demodulation units 105-1 to 105-N with tap coefficients that reflect the characteristics of the weighting coefficients in the frequency domain. It is possible to obtain the same effect as that obtained by the synthesis process.

  However, in the present embodiment, the delay in the main line system that passes the signal to be relayed is only caused by the FIR filters 901-1 to 901-N, and therefore, in principle, such as in FIG. Compared to the configuration, the processing time is short, and the processing delay can be kept within the OFDM guard time. By adopting such a configuration, it is possible to construct a single frequency network (SFN) by relaying broadcast waves, leading to an improvement in frequency utilization efficiency.

  In addition, since an FIR filter and IFFT are required for each branch, the circuit scale is slightly increased, but the frequency required to construct a broadcasting network can be saved, which is preferable.

  Moreover, it is also suitable to use with a sneak canceller that can effectively cancel a sneak wave generated when an SFN is constructed by relaying a broadcast wave.

  Thus, according to the present embodiment, the multiplication unit 110 obtains a weighting factor for each subcarrier reflecting the signal strength at the time of reception, and the FIR filters 901-1 to 901 -N use this weighting factor to receive the signal at the time of reception. Since the composite signal for each subcarrier that reflects the signal strength is obtained, the OFDM relay apparatus 900 that can obtain the composite signal for each subcarrier that also reflects the signal strength during reception can be realized with a short processing delay. .

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications.

  In one aspect of the OFDM receiver of the present invention, an automatic is provided corresponding to each of the plurality of antennas and each antenna branch, and controls the gain of the antenna reception signal so that the power of the antenna reception signal is constant. Gain control means, analog / digital conversion means for analog / digital conversion of the output of the automatic gain control means, orthogonal demodulation means for orthogonal demodulation of the output of the analog / digital conversion means, and output of the orthogonal demodulation means for frequency A plurality of antenna branch processing units each having a Fourier transform means for transforming into a region, and propagation path estimation for estimating a propagation path characteristic in the frequency domain of each antenna branch based on an output signal of the Fourier transform means of each antenna branch processing unit Means and output signal of propagation path estimation means and / or each antenna branch Signal quality estimating means for estimating the signal quality of each antenna branch based on the output signal of the Fourier transform means of the logic unit, the propagation path characteristics of each antenna branch obtained by the propagation path estimating means, and the signal quality estimating means. Multiplying means for multiplying the corresponding signal quality of each antenna branch between corresponding branches, and combining means for weighting and combining the output signals of the Fourier transform means of the plurality of antenna branch processing units based on the multiplication results obtained by the multiplying means The structure which comprises these is taken.

  According to this configuration, the signal quality estimation means obtains the signal strength at the time of reception of each branch lost due to gain control by the automatic gain control means, and the multiplication means reflects the signal strength at the time of reception. Since the weighting coefficient for each subcarrier is obtained, the combining unit obtains a combined signal for each subcarrier that reflects the signal strength at the time of reception.

  In one aspect of the OFDM receiver of the present invention, the signal quality estimation means inputs the output signal of each Fourier transform means and the output signal of the propagation path estimation means, and the distortion component of the output signal of each Fourier transform means, A configuration is adopted in which compensation is performed using the output signal of the propagation path estimation means, and the signal quality of each antenna branch is obtained based on the distance from the ideal signal point in the compensated signal.

  According to this configuration, since the signal quality of each antenna branch is obtained using the output signal of the Fourier transform means, the signal quality of each antenna branch can be obtained with high accuracy. As a result, the combining unit can obtain a combined signal for each subcarrier in which the signal strength at the time of reception is more accurately reflected. Furthermore, it is possible to minimize the influence of interference and the like that cannot be determined only by the received signal strength, and it is possible to perform synthesis that is resistant to interference and the like.

  In one aspect of the OFDM receiver of the present invention, the signal quality estimation means receives the output signal of each Fourier transform means, and performs the second Fourier transform means for Fourier transforming only the pilot carrier signal; Square means for squaring the output of the Fourier transform means, comparison means for comparing the output of the square means with a preset threshold value, accumulation means for accumulating values below the threshold in the comparison means, and the accumulation means And a reciprocal number calculating means for obtaining a reciprocal number of the output.

  According to this configuration, the signal quality of each antenna branch can be obtained with high accuracy by the signal quality estimation means.

  In one aspect of the OFDM receiver of the present invention, an automatic is provided corresponding to each of the plurality of antennas and each antenna branch, and controls the gain of the antenna reception signal so that the power of the antenna reception signal is constant. Gain control means; first analog / digital conversion means for analog / digital conversion of the output of the automatic gain control means; orthogonal demodulation means for orthogonal demodulation of the output of the first analog / digital conversion means; A plurality of antenna branch processing units having Fourier transform means for converting the output of the demodulation means into the frequency domain, and propagation path characteristics in the frequency domain of each antenna branch based on the output signal of the Fourier transform means of each antenna branch processing unit; Channel estimation means for estimating the A second analog / digital conversion means for analog / digital conversion of the control voltage in the control means; a propagation path characteristic of each antenna branch obtained by the propagation path estimation means; and a second analog / digital conversion means obtained by the second analog / digital conversion means. Multiplying means for multiplying the control voltage data of the antenna branch between corresponding branches; and combining means for weighting and combining the output signals of the Fourier transform means of the plurality of antenna branch processing units based on the multiplication results obtained by the multiplying means; The structure which comprises is taken.

  According to this configuration, the second analog / digital conversion means obtains control voltage data corresponding to the signal strength at the time of reception of each branch lost due to gain control by the automatic gain control means, and the multiplication means Since the weighting factor for each subcarrier reflecting the signal strength at the time of reception is obtained, the synthesis unit obtains the synthesized signal for each subcarrier that also reflects the signal strength at the time of reception.

  In one aspect of the OFDM receiving apparatus of the present invention, a configuration is adopted in which a conversion table for compensating for individual differences of the automatic gain control means is further provided after the second analog / digital conversion means.

  According to this configuration, even when the gain control of the automatic gain control means varies due to individual differences, the control voltage data from the second analog / digital conversion means is corrected by the conversion table and then input to the multiplication means. As a result, the multiplication means can obtain a weighting factor that well reflects the signal strength at the time of reception regardless of variations in the automatic gain control means.

  In one aspect of the OFDM receiver of the present invention, a plurality of conversion tables for compensating for individual differences of the automatic gain control means corresponding to a plurality of temperatures at the subsequent stage of the second analog / digital conversion means, and a temperature And a switching unit that switches a conversion table to be used among a plurality of conversion tables.

  According to this configuration, even when the gain control of the automatic gain control means varies according to the temperature, the control voltage data from the second analog / digital conversion means is converted into the conversion table according to the temperature switched by the switching means. After being corrected by the above, the multiplication means is input to the multiplication means, so that the multiplication means can obtain a weighting factor that well reflects the signal strength at the time of reception regardless of variations in temperature of the automatic gain control means. .

  In one aspect of the OFDM signal relay device of the present invention, the OFDM receiver, an inverse Fourier transform unit that performs an inverse Fourier transform on a signal that is provided at a subsequent stage of the OFDM receiver and is synthesized by the synthesis unit, and an inverse Fourier transform unit Modulation means for orthogonally modulating the output of the output, analog / digital conversion means for analog / digital conversion of the output of the orthogonal modulation means, transmission conversion means for converting the output of the analog / digital conversion means into a radio frequency band, and transmission conversion And an antenna for transmitting the output of the means.

  According to this configuration, the relay signal is formed based on the combined signal for each subcarrier that reflects the signal strength at the time of reception, which is obtained by the combining means, and therefore transmits a high-quality relay signal. Will be able to.

  In one aspect of the OFDM signal relay apparatus of the present invention, the gain of the antenna reception signal is controlled so that the power of the antenna reception signal is constant, provided corresponding to each of the plurality of antennas and each antenna branch. Automatic gain control means, first analog / digital conversion means for analog / digital conversion of the output of the automatic gain control means, orthogonal demodulation means for orthogonal demodulation of the output of the first analog / digital conversion means, A plurality of antenna branch processing units having Fourier transform means for converting the output of the orthogonal demodulation means into the frequency domain, and propagation paths in the frequency domain of each antenna branch based on the output signal of the Fourier transform means of each antenna branch processing unit Propagation path estimation means for estimating characteristics, output signal of propagation path estimation means and / or each Signal quality estimation means for estimating the signal quality of each antenna branch based on the output signal of the Fourier transform means of the antenna branch processing unit, and propagation path characteristics and signal quality estimation means of each antenna branch obtained by the propagation path estimation means Multiplication means for multiplying the corresponding signal quality of each antenna branch between corresponding branches, and a plurality of inverse Fourier transform means for converting the multiplication result signals corresponding to each branch obtained by the multiplication means to the time domain, respectively. A plurality of finite impulse response filters each of which receives the output of the orthogonal demodulation means of each antenna branch and uses the output of the inverse Fourier transform means as a coefficient input; and an addition means for adding the outputs of the plurality of finite impulse response filters; Orthogonal modulation means for orthogonally modulating the output of the adding means, and orthogonal modulation means A second analog / digital conversion means for digital / analog conversion of the output, a transmission conversion means for converting the output of the second analog / digital conversion means to a radio frequency band, an antenna for transmitting the output of the transmission conversion means, The structure which comprises is taken.

  According to this configuration, a weighting factor for each subcarrier in which the signal strength at the time of reception is reflected by the multiplication unit is obtained, and for each subcarrier in which the signal strength at the time of reception is also reflected by the finite impulse response filter using this weighting factor. Thus, it is possible to obtain a composite signal for each subcarrier reflecting the signal strength at the time of reception with a short processing delay.

  The OFDM receiver and OFDM signal relay apparatus according to the present invention are small and can ensure good reception quality and relay quality, and are useful when applied to radio communication equipment and broadcast equipment.

FIG. 1 is a block diagram showing a configuration of an OFDM receiving apparatus according to Embodiment 1 of the present invention. FIG. 3 is a block diagram illustrating another configuration example of the OFDM receiving apparatus according to the first embodiment. Block diagram showing a configuration example of a signal quality estimation unit FIG. 3 is a block diagram showing a configuration of an OFDM receiving apparatus according to the second embodiment. FIG. 6 is a block diagram showing a configuration for compensating for a control voltage error according to the second embodiment. FIG. 6 is a block diagram showing a configuration for compensating for a control voltage error according to the second embodiment. Block diagram showing a configuration of an OFDM relay apparatus according to Embodiment 3 FIG. 9 is a block diagram illustrating another configuration example of the OFDM relay apparatus according to the third embodiment. Block diagram showing a configuration of an OFDM relay apparatus according to a fourth embodiment

Explanation of symbols

100, 200, 400 OFDM receivers 101-1 to 101-N reception antennas 102-1 to 102-N reception conversion units 103-1 to 103-N automatic gain control units (AGC)
104-1 to 104-N, 401, 603 Analog / digital converter (A / D)
105-1 to 105-N Orthogonal demodulation unit 106-1 to 106-N, 301 Fast Fourier transform unit (FFT)
DESCRIPTION OF SYMBOLS 107 Synthesis | combination part 108 Propagation path estimation part 109 Signal quality estimation part 110 Multiplication part 302 Squared part 303 Comparison part 304 Threshold setting part 305 Accumulation part 306 Reciprocal number calculation part 501-1-501-N, 601 Conversion table 602 Temperature sensor 604 switching Unit 700, 800, 900 OFDM relay device 701, 903-1 to 903-N Inverse discrete Fourier transform unit (IFFT)
702 Quadrature modulation unit 703 Digital / analog conversion unit (D / A)
704 Transmission conversion unit 705 Transmission antenna 801 Determination unit 901-1 to 901 -N FIR filter 902 Addition unit BR- 1 to BR-N Branch processing unit

Claims (8)

Multiple antennas,
An automatic gain control unit that is provided corresponding to each antenna branch and controls the gain of the antenna reception signal so that the power of the antenna reception signal is constant, and the output of the automatic gain control unit is analog / digital converted. A plurality of antenna branch processing units having analog / digital conversion means, orthogonal demodulation means for orthogonally demodulating the output of the analog / digital conversion means, and Fourier transform means for converting the output of the orthogonal demodulation means into the frequency domain; ,
Propagation path estimation means for estimating propagation path characteristics in the frequency domain of each antenna branch based on the output signal of the Fourier transform means of each antenna branch processing unit;
Signal quality estimating means for estimating the signal quality of each antenna branch based on the output signal of the propagation path estimating means and / or the output signal of the Fourier transform means of each antenna branch processing unit;
Multiplication means for multiplying the corresponding branch characteristics by the propagation path characteristics of each antenna branch obtained by the propagation path estimation means and the signal quality of each antenna branch obtained by the signal quality estimation means;
An OFDM receiver comprising: combining means for weighting and combining the output signals of the Fourier transform means of the plurality of antenna branch processing units based on the multiplication results obtained by the multiplication means. The signal quality estimation means inputs the output signal of each Fourier transform means and the output signal of the propagation path estimation means, and outputs the distortion component of the output signal of each Fourier transform means as the output signal of the propagation path estimation means. The OFDM receiver according to claim 1, wherein the signal quality of each antenna branch is obtained based on a distance from an ideal signal point in the compensated signal. The signal quality estimation means receives the output signals of the respective Fourier transform means, a second Fourier transform means for Fourier transforming only the pilot carrier signal, and a square for squaring the output of the second Fourier transform means. Means, a comparing means for comparing the output of the square means with a preset threshold value, an accumulating means for accumulating a value equal to or less than the threshold value in the comparing means, and an inverse number calculating means for obtaining an inverse number of the output of the accumulating means, The OFDM receiver according to claim 1. Multiple antennas,
An automatic gain control unit that is provided corresponding to each antenna branch and controls the gain of the antenna reception signal so that the power of the antenna reception signal is constant, and the output of the automatic gain control unit is analog / digital converted. A plurality of first analog / digital conversion means, orthogonal demodulation means for orthogonally demodulating the output of the first analog / digital conversion means, and Fourier transform means for converting the output of the orthogonal demodulation means into the frequency domain. An antenna branch processing unit of
Propagation path estimation means for estimating propagation path characteristics in the frequency domain of each antenna branch based on the output signal of the Fourier transform means of each antenna branch processing unit;
Second analog / digital conversion means for analog / digital conversion of a control voltage in the automatic gain control means of each antenna branch processing unit;
Multiplication means for multiplying the propagation path characteristics of each antenna branch obtained by the propagation path estimation means and the control voltage data of each antenna branch obtained by the second analog / digital conversion means between corresponding branches. ,
An OFDM receiver comprising: combining means for weighting and combining the output signals of the Fourier transform means of the plurality of antenna branch processing units based on the multiplication results obtained by the multiplication means. The OFDM receiver according to claim 4, further comprising a conversion table for compensating for individual differences of the automatic gain control means after the second analog / digital conversion means. Subsequent to the second analog / digital conversion means, a plurality of conversion tables for compensating for individual differences of the automatic gain control means corresponding to a plurality of temperatures, and use of the plurality of conversion tables according to the temperature The OFDM receiving apparatus according to claim 4, further comprising switching means for switching the conversion table. The OFDM receiver according to any one of claims 1 to 6,
An inverse Fourier transform unit that is provided at a subsequent stage of the OFDM receiver and performs an inverse Fourier transform on the signal synthesized by the synthesis unit;
Orthogonal modulation means for orthogonally modulating the output of the inverse Fourier transform means;
Analog / digital conversion means for analog / digital conversion of the output of the orthogonal modulation means;
Transmission conversion means for converting the output of the analog / digital conversion means into a radio frequency band;
An OFDM signal relay apparatus comprising: an antenna that transmits the output of the transmission conversion means. Multiple antennas,
An automatic gain control unit that is provided corresponding to each antenna branch and controls the gain of the antenna reception signal so that the power of the antenna reception signal is constant, and the output of the automatic gain control unit is analog / digital converted. A plurality of first analog / digital conversion means, orthogonal demodulation means for orthogonally demodulating the output of the first analog / digital conversion means, and Fourier transform means for converting the output of the orthogonal demodulation means into the frequency domain. An antenna branch processing unit of
Propagation path estimation means for estimating propagation path characteristics in the frequency domain of each antenna branch based on the output signal of the Fourier transform means of each antenna branch processing unit;
Signal quality estimating means for estimating the signal quality of each antenna branch based on the output signal of the propagation path estimating means and / or the output signal of the Fourier transform means of each antenna branch processing unit;
Multiplication means for multiplying the corresponding branch characteristics by the propagation path characteristics of each antenna branch obtained by the propagation path estimation means and the signal quality of each antenna branch obtained by the signal quality estimation means;
A plurality of inverse Fourier transform means for transforming a multiplication result signal corresponding to each branch obtained by the multiplication means into the time domain, and
A plurality of finite impulse response filters each of which receives the output of the orthogonal demodulation means of each antenna branch and receives the output of the inverse Fourier transform means as a coefficient input;
Adding means for adding outputs of the plurality of finite impulse response filters;
Orthogonal modulation means for orthogonally modulating the output of the adding means;
Second analog / digital conversion means for digital / analog conversion of the output of the quadrature modulation means;
Transmission conversion means for converting the output of the second analog / digital conversion means into a radio frequency band;
An OFDM signal relay apparatus comprising: an antenna that transmits the output of the transmission conversion means.

Images